I. Field of the Invention
This invention relates generally to a method of producing a superior quality of glass or other brittle material resulting in an end product which is substantially stronger than conventional glass or other brittle material and exhibits greater strength consistency than was previously known. Which is a continuation-in-part of copending application Ser. No. 06/868,829 filed on May 29, 1986.
II. Description of the Prior Art
In the past, "tempered" glass was used for strong part requirements. Over the years, a process known variously as "chemical tempering", "ion exchange", or "chemical strengthening" came to be employed to do the same thing. These processes render the outside of a glass in compression while the inside is in tension. "Tempering" in glass is not the same as in metals. It merely consists of rapid cooling (actually "quenching") from the melt, or other high temperature, which causes the outside skin to "solidify" first (glass is a technical liquid of nearly infinite viscosity, not a solid), "Chemical" tempering or "ion exchange" or "chemical strengthening" accomplishes the same result by replacing, for example, sodium ions with "fatter" potassium ions in the surface region. This squeezes the surface together, causing compression there. When the glass beam is bent, the tension side first has to lose all the residual compression before going into tension. Either process can result in a part acting as if it could survive between 30,000 psi and 45,000 psi in tension (instead of just bending, alone). Some parts have approached 60,000 psi in this way, but in thick section only, and not reliably or repeatedly.
The compressive strength of glass is not usually a problem. This is primarily due to the fact that existing flaws and micro cracks in the surface do not propagate under compressive stress. Compressive strengths of 250,000 psi are commonly observed.
One problem with the prior art is that it is not reliable statistically. The distribution of yield point for known glass is skewed, with a long tail off in the high strength direction and a short cutoff at lower values. Thus, one can reliably count on achieving only a fraction of the attainable value in tension.
Throughout this disclosure, the term "glass" is intended to mean not only those materials commonly known as glass, but also ceramics, and vitreous materials and other substitutes therefor. It even applies to some "metals" (e.g., germanium, and silicon).